The present invention relates generally to an apparatus for braking an elevator car consisting of a brake unit with at least one brake cylinder and a slidable piston in the brake cylinder for the braking and holding of the elevator car, where the piston, in the case of braking, can be operated by a spring generating a spring tension and wherein the spring acts against a pressure medium.
In the Swiss patent document CH 440 614, a safety brake for elevators with cable drive is shown, in which the braking force is generated independently of the driving means as, for example, electrical current, compressed air, or pressured oil. The braking force is produced by springs, which work against the force of a brake release cylinder. In the released state of the brake, the brake release cylinder is constantly acted upon by a working fluid. In case of failure of the pressure unit, the spring force alone is active and thus the safety braking is assured.
A disadvantage of this known equipment is the fact that the safety braking force produced by the springs has to be opposed constantly by an at least equally large force produced by the drive means in the brake release cylinder, so that the brake remains released under normal conditions.